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Application!of!slingshot!model!to!the!giant!radio!galaxy!DA240!
(Brief!:!DA!240!in!slingshot!model)!
by!
S.!Muthumeenal!&!Dilip!G!Banhatti@!
@[dilip.g.banhatti@gmail.com]!
School!of!Physics,!Madurai!Kamaraj!University,!Madurai!625021,!India!
!
Abstract! /! Summary.! We! attempt! a! slingshot! model! interpretation! of! the! unusual!
association! of! some! 1&1/3! dozen! nonstellar! galaxian! objects! around! the! parent! optical!
galaxy!of!the!giant!radio!galaxy!DA!240!(=!0748.6+55.8!(J2000)).!Similar! interpretation!may!
be!possible!for!another!large!radio!galaxy!3C!31!(=!NGC!383!=!0104.6+32.1!(1950.0)).!
Keywords.!active!galaxy!–!radio!galaxy!–!beam!model!–!slingshot!model!
Motivation.!Spectroscopic!observations!of!most!of!the!32!optical!objects!brighter!than!about!
16!mag!within! half! a! degree! of!DA! 240! parent! galaxy! have! been! reported! by! Peng! et! al!
(2004).!Sixteen!objects! show!nearly! the! same! redshift!as! the!DA!240!parent! (z!=!0.0358).!
Most! of! the! others! have! lower! redshifts,! and! are! probably! outlying!members! of! Zwicky!
cluster! Zw! 0756.1+5616.! The! objects!with! nearly! DA! 240! redshift! show! significant! radio!
emission,!are!mostly!along!DA!240!radio!major!axis,!and!their!redshifts!systematically!vary!
along!this!axis,!implying!dynamical!time!scale!of!1!Gyr.!Interpretation!within!beam!model!of!
active! galaxies! runs! into!problems!on! several! counts,!while! the!unusual! features!of! these!
observations!fit!quite!naturally!into!slingshot!model.!
Beam!and!slingshot!models!for!active!galaxies.!In!beam!model!(e.g.,!Begelman!et!al!1984!&!
references! therein)! the!central! ‘engine’!harbours!a!deep!gravitational!potential! (possibly!a!
supermassive!spinning!black!hole)!which!generates!twin!oppositely!directed!magnetoplasma!
beams!or! jets! along! the!black!hole! accretion!disk! spin! axis,! travelling!with! at! least!mildly!
relativistic!bulk!speed.!The!observed!structures!in!active!galaxies!and!their!nuclei!arises!from!
the! interaction! of! these! hydromagnetic! jets! progressively! with! the! surrounding! nuclear,!
interstellar! and! intergalactic! /! intracluster! media.! The! highly! relativistic! magnetoplasma!
particles!emit!mainly!nonthermal!radiation!in!the!entrained!magnetic!field.!This!synchrotron!
radiation! is! observed! in! different! polarizations! and! from! x"ray! to! radio! part! of! the!
electromagnetic! radiation! spectrum,! but! mainly! in! radio.! (See! e.g.,! Banhatti! 1998! &!
references! therein.)! A! double! radio! galaxy! emits! predominantly! radio! energy! from! two!
elongated!regions!called!radio!lobes,!one!on!each!of!two!sides!of!the!optical!parent!galaxian!
object.!Bulk! supersonic! speeds!of! the! twin! jets! through! the! surrounding!medium! leads! to!
shocks!creating!radio!hotspots,!especially!at!radio!lobe!ends.!
In! slingshot!model! (Saslaw!et!al!1974)! the!densely!populated! supermassive!active!galactic!
nucleus! ejects! two! or!more!massive! objects! or! black! holes! in! two! diametrically! opposite!
directions!due!to!gravitational!dynamical! instability.!The!black!hole!trajectories!are!seen!as!
jets!and! lobes.!The!black!holes!may!escape!from!the!supermassive!galaxian!nucleus!or!may!
oscillate!relative!the!nucleus.!(See,!e.g.,!Banhatti!1998!&!references!therein.)!
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Basic!differences!between!beam!and! slingshot!models! :! (1)! In! slingshot!model! the!ejected!
black! holes!move! substantially,!while! beam!model! has! a! single! black! hole! (or! possibly! a!
binary)!more!or! less! stationary! at! the!nucleus.! (2)! In! the! twin!beam!model! the! source!of!
energy! remains! in! the! active! galactic! nucleus! of! the! (extended)! radio! galaxy,! the! energy!
being!transported!continuously!to!the! lobes,!which!can!be!very!far!away!from!the!nucleus,!
while!in!slingshot!model!the!sources!of!energy!are!massive!black!hole!accretion!disk!systems!
which!move! within! the! lobes! as! they! locally! emit! synchrotron! energy,! so! that! no! long!
distance!energy!transport!is!needed!in!this!‘dressed!slingshot’!(Lin!&!Saslaw!1977).!
Slingshot!model!details!and!application!to!some!radio!galaxies.!This!section!briefly!presents!
some! relevant! details! of! slingshot!model! and! its! application! to! some! radio! galaxies.! The!
literature!used!for!this!survey:!Valtonen!(1979,!1999),!Valtonen!&!Heggie!(1978),!Bridle!et!al!
(1989),!Mikkola!&!Valtonen! (1990),!Borcherds!&!McCauley! (1993),!Valtonen! et! al! (1994),!
Valtonen!&!Heinämäki!(2000).! In!slingshot!model!supermassive!black!holes!are!thrown!out!
from!an!active!galaxian!nucleus!(AGN)!via!the!gravitational!3"body!process.!Conserving!linear!
momentum,! a! single! black! hole! escapes! in! one! direction! and! a! binary! in! the! opposite!
direction,!each!producing!radio!emission!along! its!trajectory.!Numerically! integrating!orbits!
in!the!model!AG(N)!potential!and!fitting!simple!functions!through!the!computed!points!one!
gets!
(r!/!r0!)!=!(2.89!–!2.4!((t/t0!)!–!1)2)1/2!–!0.7!,!!!!!!0!<!(t!/!t0!)!<!2!
where!r!is!the!distance!from!the!AGN,!and!!
r0!=!0.85!{1"!(Ve/Vesc)!2}"5/3!(M/(3!x!1012!M))!Kpc,!
t0!=!0.75!(r0/Kpc)!1.3!(M/(3!x!1012!M ))"0.25!Myr.!
M!is!the!AGN!mass!and!M !is!the!solar!mass.!The!escape!velocity!is!
Vesc!=!3110!(M/(3!x!1012!M ))!0.25!km/s!
These!expressions!are!within!10%!of!numerically!calculated!orbits!for!0.8!#! (Ve/Vesc)!<!1.!Different!
radio!sources!modeled!in!slingshot!theory!include!3C!465,!3C!83.1B,!3C!288,!3C!277.3,!3C!388,!Cen!A,!
3C!390.3,!3C!405,!3C!219,!3C!129!and!3C!274.!The!dynamical!time!scales!needed!are!10!Myr!to!1!Gyr.!
Schematic!orbits!are!shown!as! line!diagrams.!Convolution!with!appropriate!emission!function!gives!
radio!brightness!distribution.!(See!the!references!listed!earlier.)!
Beam! and! slingshot!models! for! double! radio! sources.! In! beam! theory! large! scale! jets! represent!
particle!flow!channels,!while!in!slingshot!model!they!are!trails!left!behind!by!the!outgoing!black!hole!
and! its!backward!pointing!beam.!Trails!are!pressure!confined!and!essentially!stationary,!while! flow!
channels!are!seen!as!dynamic!entities.!
The! frequency!of!detecting! jets!and!counter"jets! in!double! radio!galaxies!and!quasars!goes!against!
the!simplest!versions!of!beam!model,!while!it!can!be!readily!explained!in!slingshot!model.!
Jets!which!do!not!originate!from!the!galactic!nucleus!(e.!g.,!3C!338)!are!problematic!in!beam!model!
but!are!expected!in!slingshot!model.!!
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Double!hotspots!in!radio!lobes!sometimes!present!a!problem!in!beam!theory,!especially!when!there!
are!indications!of!current!particle!acceleration!in!both!hotspots.!!In!slingshot!model!double!hotspots!
are!a!standard!feature.!!!
The!alignment!of!hotspots!across!the!nucleus!of!the!galaxy!is!good!in!view!of!the!jets!and!the!off"axis!
positions!of!the!hotspots.!This!gives!a!strong!indication!that!hotspots!are!the!primary!movers!and!jets!
are!only!secondary!phenomena.!This!is!so!in!slingshot!model!but!not!in!beam!model.!!
The!advantage!of!slingshot!model! is! that! it! is!an! integral!part!of! the!general!body!of!astrophysical!
theory!which!describes!the!merger"evolution!of!galaxies!in!cosmological!setting.!Therefore,!it!is!fully!
calculable!and!results!may!be!directly!compared!with!observations.!
DA!240!features!which!call!for!slingshot!model.!!
(1)The!nonstellar!galaxian!objects!along!DA!240!radio!major!axis!must!be!interpreted!in!beam!model!
as!members!of!the!same!group!of!galaxies!as!the!DA!240!parent.!Polarization!observations!of!DA!240!
lobes! imply!number!density!n! $!10"5! /cc!which! is! too! low! for!galaxy! formation.! In! slingshot!model!
these!massive!objects!have!been!flung!out!from!the!DA!240!AGN,!and!are!at!different!points!of!the!
orbit(s),!so!can!be!in!any!region,!of!high!or!low!density.!
(2)Both!DA!240! lobes!have!roughly!symmetrically!placed!hotspots,!but!they!are!very!asymmetric! in!
strength,!the!eastern!one!about!50!times!brighter!than! its!western!counterpart.!The!reason!for!this!
brightness! contrast! is! unclear! in! beam!model.! In! slingshot! theory! the! hotspots! are! dressed! black!
holes! (Lin!&!Saslaw!1977),! symmetrically!placed!due! to! linear!momentum!balance,!with! their!own!
twin"jet!systems!that!may!have!very!different!synchrotron!emissivities.!
(3)Of!the!16!nonstellar!galaxian!objects!with!redshifts!similar!to!DA!240!parent,!10!are!aligned!along!
the! radio! lobes! while! 6! lie! along! roughly! orthogonal! axis.! In! beam! theory! there! is! no! direct!
connection!between!this!grouping!and!the!radio!galaxy!jets!or!beams.!In!slingshot!theory!there!is!an!
orbital!plane!with! concentration!near! the!AGN,! and!due! to!orbital! instability,!massive!objects! are!
ejected! in!a!narrow!cone!normal!to!and!on!both!sides!of!the!central!flat!nuclear!concentration.!For!
such!a!scenario!for!DA!240,!the!6!objects!/!galaxies!that!lie!in!directions!roughly!normal!to!the!double!
radio! source!axis! should!be!by! far! the!more!massive! component!of! the! total!mass!of! the!DA!240!
group.!Perhaps!this!can!be!verified!by!future!spectroscopic!mass!estimates.!
(4)Monte!Carlo!simulations!show! that! the!chance! that!17!objects!are!aligned!as!observed! is!about!
3×10"4,! indicating! a! causal! connection,!mysterious! in! beam!model,! but! quite! natural! in! slingshot!
mechanism.!A!stable!dynamical!axis!over! time!scale!much! longer! than!synchrotron!emission!age! is!
also!consistent!with!slingshot!model.!
(5)Projecting!onto! the! radio!major!axis! the! location!of!each!of!11!objects!on!or!near! the!axis,!and!
plotting!the!redshift!difference!relative!to!the!median!as!%v!vs!the!distance!D!along!the!axis!gives!a!
correlation!of!slope!%v/D!$!425!km/s/Mpc,!with!correlation!coefficient!"0.74!(Peng!et!al!2004).!This!
calls! for! an! explanation,! not! naturally! possible! in! beam! theory,! but!maybe! possible! in! slingshot!
model.!
Acknowledgements.! The!work! reported! here! formed! part! of! S.!Muthumeenal’s!M.Phil.! project! in!
2007.!DGB!thanks!UGC,!New!Delhi!for!financial!support.!
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References!
#!Banhatti,!D!G!1998!Phys!Rep!303!81"182!Bilateral!symmetry!in!active!galaxies!
#!Begelman,!M!C!et!al!1984!Rev!Mod!Phys!56!255"351!...!!
#Borcherds,! P! H! &!McCauley,! G! P! 1993! ...!…! The! gravitational! 3"body! problem! :! optimizing! the!
slingshot!
#!Bridle,!A!H!et!al!1989!AJ!97!674"85!The!unusual!radio!galaxy!3C!288!
#!Lin,!D!N!C!&!Saslaw,!W!C!1977!ApJ!217!958"…!…!
#!Mikkola,!S!&!Valtonen,!M!V!1990!ApJ!348!412"20!Slingshot!ejections!in!merging!galaxies!
#! Peng,! B! et! al! 2004! A&A! 415! 486"98! Galaxies! around! the! giant! double! radio! source! DA! 240! –!
Redshifts!and!the!discovery!of!an!unusual!association!
#!Saslaw,!W!C!et!al!1974!ApJ!190!253"70!The!gravitational!slingshot!and!the!structure!of!extragalactic!
radio!sources!
#!Valtonen,!M!J!1979!ApJ!227!L79"83!Brightness!and!shape!of!radio!jets!
#!Valtonen,!M! J!1999!ApJ!520!97"104! Jets,!hotspots!and! sidedness! in!double! radio! sources! in! the!
slingshot!theory!
#!Valtonen,!M!J!&!Heggie,!D!C!1978!…!3"body!gravitational!scattering!:!comparison!between!theory!
and!experiment!
#!Valtonen,!M!J!et!al!1994!ApJ!Supl!95!69"86!Slingshot!ejections!from!clusters!of!3!and!4!black!holes!
#!Valtonen,!M!J!&!Heinämäki,!P!2000!...!...!Double!radio!sources!:!two!approaches!
! ! ! ! ! ! "x"0"x"!
